Field of the Invention
The present invention relates to a video data recording and reproducing apparatus for recording in an overlapping manner new video data on a video tape (VTR tape) or other tape recording medium on which video data has been already recorded and to a method of the same.
The MPEG (Motion Picture Experts Group) system and other compression and coding systems for compressing and coding video data of a digital format in units of GOP's (group of pictures) comprised of a plurality of frames are now being put into practical use.
Digital cassette tape recorders (VCR's) able to compress and code video data by the MPEG system or the like and record the compressed video data on digital VTR tape housed in a cassette and able to reproduce, expand, and decode such recorded compressed video data are accordingly also being developed and marketed.
When editing several scenes worth of video data of a movie, it is necessary to record new compressed video data (top data) in an overlapping manner on a VTR tape on which video data compressed and coded in units of GOP's (bottom data) have been already recorded (perform "editing recording"). When performing such editing recording, at the boundary between the bottom data and the top data (editing point), the recording position of the boundary of the GOP's of the top data on the VTR tape and the recording position of the boundary of the bottom data must be accurately matched or else part of the bottom data will be lost and the quality of the video after reproduction will be lowered. Accordingly, when performing such editing recording, it is necessary to record the data on the VTR tape while accurately matching the boundaries of the GOP's of the top data and bottom data at the editing point.
However, VTR tape stretches or contracts. Also, there are limits to the mechanical precision of the tape travelling systems which can be achieved among a number of VCR's. Therefore, when performing the editing recording, it is difficult to accurately match the boundaries of GOP's of the top data and bottom data at the editing point.
One idea could be to precisely control the travel of the VTR tape when performing the editing recording so as to match the boundaries of the GOP's of the bottom data and the top data at the editing point taking into consideration the stretching or contraction of the VTR tape. However, when trying to match the boundaries of the GOP's at the editing point by precision control of the travel of the VTR tape, the processing relating to the control of the travel of the tape becomes difficult and, in addition, a high mechanical precision is demanded in the tape travelling system.